<!DOCTYPE html>
<html>

<head>
  <title></title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link href="../bootstrap-5.1.3-dist/css/bootstrap.css" rel="stylesheet">
  <script src="../bootstrap-5.1.3-dist/js/bootstrap.bundle.min.js"></script>
</head>

<body class="container">
  <form action="">
    <label for="sel1" class="form-label">大号下拉菜单：</label>
    <select class="form-select form-select-lg" id="sel1" name="sellist1">
      <option>西瓜</option>
      <option>苹果</option>
    </select>
    <br>

    <label for="sel2" class="form-label">正常下拉菜单：</label>
    <select class="form-select" id="sel2" name="sellist2">
      <option>西瓜</option>
      <option>苹果</option>
    </select>

    <label for="sel3" class="form-label">小号下拉菜单：</label>
    <select class="form-select form-select-sm" id="sel3" name="sellist3">
      <option>西瓜</option>
      <option>苹果</option>
    </select>
    <button type="submit" class="btn btn-primary mt-3">提交</button>
  </form>

</body>

</html>